1. Field of the Invention
The present invention relates to a hard disk drive (HDD) and, more particularly, to a hub assembly mountable on an off-line servo-track writer as well as on a spindle motor, a spindle motor including the hub assembly, and a method for servo-track writing.
2. Description of the Related Art
Hard disk drives (HDDs), which store information in computers, reproduce or record data on a rotating disk using a read/write head. In the HDDs, the read/write head functions by being moved to a desired position by an actuator while being lifted above a recording surface of the rotating disk at a predetermined height.
FIG. 1 is an exploded perspective view of a conventional HDD.
Referring to FIG. 1, a base member 11 of the HDD supports a spindle motor 30 for rotating disks 21 and 22 that are data recording media, and an actuator 40 for moving a read/write head for reproducing and recording data at a desired position on the disks 21 and 22.
The spindle motor 30 is installed on the base member 11. The two disks 21 and 22 may be mounted on the spindle motor 30 as shown in FIG. 1, and one, or three or more disks may also be mounted. If the plurality of disks 21 and 22 are mounted on the spindle motor 30, a ring-shaped spacer 50 is interposed between the disks 21 and 22 to maintain an interval between the disks 21 and 22. A clamp 60 is coupled to a top portion of the spindle motor 30 using a screw 70 to firmly fix the disks 21 and 22 to the spindle motor 30.
The actuator 40 includes a swing arm 42 rotatably coupled to a pivot 41 installed on the base member 11, a suspension 43 installed on an end of the swing arm 42 and adapted to elastically bias a slider on which the read/write head is mounted toward a surface of one of the disks 21 and 22, and a voice coil motor (VCM) 45 for rotating the swing arm 42. The VCM 45 is controlled by a servo control system, and rotates the swing arm 42 in a direction according to Fleming's Left Hand Rule due to an interaction between current input to a VCM coil and a magnetic field formed by magnets. That is, if the HDD is turned on and the disks 21 and 22 begin to rotate, the VCM 45 rotates the swing arm 42 counterclockwise to move the read/write head over a recording surface of the respective disks 21 and 22. On the other hand, if the HDD is turned off and the disks 21 and 22 stop rotating, the VCM 45 rotates the swing arm 42 clockwise to remove the read/write head from the recording surface of one of the disks 21 and 22. At this time, the read/write head removed from the recording surface of the respective disks 21 and 22 is parked on a ramp 46 disposed outside the disks 21 and 22.
A cover member 12 is attached to an upper portion of the base member 11 using a plurality of screws 19. The base member 11 and cover member 12 enclose and protect the disks 21 and 22, the spindle motor 30, and the actuator 40.
The structure where the spindle motor 30, the disks 21 and 22, the spacer 50, and the clamp 60 are coupled to one another will now be explained in further detail with reference to FIG. 2.
Referring to FIG. 2, the spindle motor 30 includes a shaft 31 rotatably supported on the base member 11, and a stator 33 and a rotator 34 placed around the shaft 31. The rotator 34 is referred to as a hub. The data storage disks 21 and 22 are fitted to an outer periphery of the hub 34. As mentioned above, if the plurality of disks 21 and 22 are mounted on the spindle motor 30, the ring-shaped spacer 50 for maintaining an interval between the disks 21 and 22 is attached to the outer periphery of the hub 34 and interposed between the disks 21 and 22. The clamp 60 for fixing the disks 21 and 22 is coupled to a top portion of the shaft 31 using the screw 70.
In the spindle motor 30, the hub 34 rotates together with the shaft 31, and, accordingly, rotates the disks 21 and 22.
Although not shown, a shaft of the spindle motor 30 may be fixed to the base member 11. In this case, the hub 34 is rotatably coupled to the outer periphery of the fixed shaft.
In the HDD constructed as above, servo-track information is written in advance on the surfaces of the disks 21 and 22 so that the read/write head can be moved to a desired position on one of the disks 21 and 22 in a faster and more exact manner. The process of writing the servo-track information in advance is referred to as servo-track writing. The servo-track writing is typically performed after the HDD is completely assembled. That is, after the disks 21 and 22 are mounted on the spindle motor 30, servo-track information is written to the rotating disks 21 and 22 using a clock head of a servo-track writer.
However, such a servo-track writing method requires much time. In particular, the data storage capacity of a magnetic disk in a HDD has increased remarkably in recent years. Accordingly, the number of tracks on the disk increases, thereby lengthening a time required for servo-track writing and increasing production costs.
In order to solve those problems, an off-line servo-track writing method has been used recently. In this method, a plurality of disks are mounted on a separate off-line servo-track writer (OSTW) before mounting the plurality of disks on a spindle motor so that servo-track writing can be performed on the plurality of disks at once.
However, in such an off-line servo-track writing method, since the plurality of disks on which servo-track writing is completed should be individually mounted on a hub of the spindle motor, misalignment of the disks along their rotational axes and misalignment of the phases of the disks occur often and repeatable run-out (RRO) occurs on the disks during the operation of the HDD.